1. Field of the Invention
The present invention broadly relates to vane assemblies in gas turbine engines and, more particularly, is concerned with an improved mounting construction for a high pressure vane which increases the fatigue life thereof.
2. Description of the Prior Art
In conventional gas turbine engines, working medium gases are compressed in a compression section of the engine and then flowed to a combustion section where fuel is mixed with the gases and burned to add energy to the flowing medium. The high energy medium is subsequently flowed to a turbine section where a portion of the energy is extracted and applied to drive the engine compressor.
The turbine section includes a plurality of alternating rows of rotor blades and stator vanes. Each row of stator vanes directs the working medium gases to a preferred angle of entry into the downstream row of rotor blades. The rotor blades in turn extract energy from the medium gases for driving the engine compressor.
One factor limiting the life of stator vanes is low fatigue life of the material from which the respective components are fabricated due to the thermal expansion of the material during engine operation. U.S. Pat. No. 3,908,446 to Salt recognizes that fatigue life of materials used in articles, such as parts found in gas turbine engine, is affected by the design of the articles. By changing the design to reduce the stress in a critical area, the useful life of the article may be increased. The Salt patent mentions several ways to change the design of the part to reduce stress, such as by changing the contour of a fillet or by reshaping or eliminating cavities or holes.
Absent from the prior art is a simple technique for constructing a turbine vane assembly so as to accommodate thermal expansion between its parts. In some conventional constructions, all of the parts are rigidly brazed together. Alternatively, in other conventional construction the parts of the assembly may be cast together as a single, integrally-formed piece. Neither of these constructions will permit differential thermal expansion between parts without increasing the incidence of material fatigue. Consequently, a need exists for a mounting construction which accommodates for differential thermal expansion in a simple and effective manner.